Descaudatine A (1), an undescribed phenolic glycoside, along with a known analogue (2) and ten flavonoids (3-12), were isolated from the whole plant of Desmodium caudatum. Compounds 1 and 4 exhibited potent antioxidant activities with the IC 50 of 58.59 μM and 31.31 μM, respectively, which were approached to that of the positive control Vitamin C (IC 50 = 46.32 μM). Meanwhile, 12 showed moderate antioxidant activity with the IC 50 of 173.9 μM. Besides, compounds 3 and 6 inhibited the proliferation of HeLa cells with IC 50 values of 56.14 μM and 69.04 μM, respectively. Further studies indicated that 3 and 6 could dose-dependently induce PARP cleavage and might trigger caspase-3, 8, 9 activation to induce apoptosis. RXRα is an ideal anticancer target of nuclear receptor. The reporter gene assay of RXRα indicated that 3 and 6 could inhibited the 9-cis-RA induced RXRα transcription in a concentration-dependent manner.

of main observation and conclusion Oxygen atom transfer reactions between alkynes and heteroarene N-oxides are currently mediated by transition metal, such as gold, ruthenium or rhodium, but they have never been catalyzed by osmium. Herein, we report stepwise oxidations of terminal alkynes mediated by an osmium carbolong complex, using pyridine N-oxide as the oxidant, yielding novel aldehyde-or carboxylic acid-coordinated osmapentalyne derivatives selectively. The mechanism was illustrated by density functional theory calculations, providing a new route for oxygen atom transfer between heteroarene N-oxides and alkynes.

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